Oahu Amakihi

The Oahu Amakihi (Chlorodrepanis flava) is one of the last remaining native Hawaiian honeycreepers endemic to the island of O‘ahu. This small, vibrant bird has managed to survive and adapt in a rapidly changing environment, making it a subject of interest for ornithologists and bird enthusiasts alike. Despite the challenges posed by habitat loss, introduced predators, and diseases, the Oahu Amakihi shows signs of resilience, making it less vulnerable than many of its relatives. This article provides an in-depth look at the Oahu Amakihi, covering its taxonomy, distribution, behavior, feeding habits, breeding, threats, and more.

Description

The Oahu Amakihi is a small bird, measuring about 11 centimeters (4.5 inches) in length. Males are characterized by their bright yellow underparts, which sharply contrast with their greenish upper parts. Females are generally duller, with two prominent wing-bars that distinguish them from their male counterparts. The Oahu Amakihi has a slightly curved bill, which is well-adapted for its varied diet of insects and nectar.

Physical Characteristics at a Glance

The bright yellow plumage of the males makes the Oahu Amakihi a striking sight in the forests of O‘ahu, while the more subdued females blend well into the foliage.

Taxonomy

The Oahu Amakihi belongs to the family Fringillidae, which includes the true finches and Hawaiian honeycreepers. It was first described by Andrew Bloxam in 1825 during his voyage to the Hawaiian Islands aboard the HMS Blonde. Initially classified under the genus Hemignathus, the species was later reassigned to Chlorodrepanis following phylogenetic analyses of mitochondrial and nuclear DNA sequences.

Taxonomic Classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Passeriformes
• Family: Fringillidae
• Genus: Chlorodrepanis
• Species: Chlorodrepanis flava

The reclassification of the Oahu Amakihi into Chlorodrepanis aligns it with other similar honeycreepers, highlighting its evolutionary relationships within the group.

Distribution and Range

The Oahu Amakihi is endemic to the island of O‘ahu, where it is most commonly found in the wetter southern regions and the central valleys near Wahiawa and Mililani. The bird has also been observed in two major parks: the Honouliuli Preserve and the Wa‘ahila Ridge State Recreation Area.

Range and Population Estimates

The Oahu Amakihi primarily occurs at altitudes above 500 meters but can be found at lower elevations in certain valleys. Recent expansions into lower areas, where mosquito populations (vectors of avian malaria) are more common, suggest that some populations may have developed resistance to the disease.

Habitat

The Oahu Amakihi is a versatile bird that inhabits a variety of forest types on O‘ahu. It prefers native forests where koa (Acacia koa) and ‘ōhi‘a lehua (Metrosideros polymorpha) dominate, but it has also adapted to non-native forests and even wooded urban areas.

Habitat Preferences

The ability of the Oahu Amakihi to thrive in both native and non-native forests, as well as in urban areas, demonstrates its adaptability, which has likely contributed to its survival on O‘ahu.

Behavior

The Oahu Amakihi is an active and agile bird, often seen flitting through the forest canopy in search of food. It is known for its territorial behavior, especially during the breeding season when pairs defend their nesting sites vigorously.

Vocalization

The Oahu Amakihi has a distinctive song composed of a series of rapid, high-pitched notes followed by a long trill. This vocalization is used both to attract mates and to defend territory from rivals. In addition to its song, the bird also produces a variety of calls, including soft chirps and whistles, which are used for communication within pairs or flocks.

Feeding

The Oahu Amakihi has a varied diet that includes insects, nectar, and occasionally small fruits. Its slightly curved bill is well-suited for scraping off pieces of bark to reach insects hidden underneath, making up the bulk of the protein in its diet. The bird also drinks nectar from native flowers, particularly ‘ōhi‘a lehua, and has been known to use sugar feeders in urban areas.

Diet Composition

The diet of the Oahu Amakihi varies with the availability of food sources, and its adaptability in foraging likely contributes to its survival in different habitats.

Breeding

The breeding season for the Oahu Amakihi typically occurs from mid-December to early March. During this time, pairs form and establish territories in suitable nesting sites, which are usually high in the canopy of trees. The nest is small, measuring 5.1 to 10.2 cm (2-4 inches) in width, and is constructed from twigs, leaves, and other plant materials.

Breeding Characteristics

After hatching, the chicks are covered in brown down feathers. They remain in the nest for about three weeks before fledging. During this period, both parents are involved in feeding and caring for the young.

Threats

The Oahu Amakihi, like many other Hawaiian honeycreepers, faces several significant threats. Habitat loss due to urbanization and agricultural expansion has reduced the availability of suitable nesting and feeding sites. Additionally, introduced predators such as rats and mongoose pose a constant threat to nests and young birds. Avian malaria, transmitted by mosquitoes, has been particularly devastating to Hawaiian honeycreepers; however, the Oahu Amakihi appears to have developed some resistance to the disease, which may explain its persistence at lower elevations.

Key Threats to the Oahu Amakihi

Despite these challenges, the Oahu Amakihi has shown a remarkable ability to adapt, particularly in urban and mixed forest environments.

Migration and Movements

The Oahu Amakihi is a non-migratory species, although it may exhibit some altitudinal movements in response to seasonal changes in food availability. During the breeding season, the bird remains close to its nesting sites, but outside of this period, it may move to different parts of its range to exploit available food resources.

Conservation Status

The Oahu Amakihi is currently listed as “Vulnerable” by the IUCN due to its relatively stable population compared to other Hawaiian honeycreepers. While it faces significant threats, particularly from habitat loss and disease, its adaptability has allowed it to maintain a presence on O‘ahu, making it one of the few honeycreepers that is not classified as critically endangered.

Conservation Strategies

• Habitat Protection: Efforts are focused on preserving and restoring native forests, particularly in the southern and central regions of O‘ahu.
• Invasive Species Control: Predator control programs and fencing are essential for protecting nesting sites.
• Disease Management: Continued research into the bird’s resistance to avian malaria and efforts to control mosquito populations are crucial for its long-term survival.
• Public Education: Raising awareness about the importance of preserving native bird species and their habitats is key to ensuring ongoing conservation support.

Conclusion

The Oahu Amakihi is a resilient and adaptable bird that has managed to survive in the face of significant environmental challenges. Its ability to thrive in a variety of habitats, coupled with its apparent resistance to avian malaria, offers hope for its continued survival. However, ongoing conservation efforts are essential to ensure that this unique Hawaiian honeycreeper continues to flourish on the island of O‘ahu. By protecting its habitats and addressing the threats it faces, we can help preserve the rich biodiversity of Hawaii for future generations.